Reverberation is the phenomenon of sound persistence in an enclosed space after the sound source stops. It is caused by multiple reflections of sound off walls, floor, ceiling, and objects. The reverberation time characterizes the acoustics of a room.
Discover FizziQ
How to measure it in class
With the FizziQ app, it is possible to measure the reverberation time of a room.
Steps:
- Open FizziQ and select the “Sound Level Meter” or “Recorder” instrument
- Position yourself in the center of the room to study
- Produce a brief, loud sound (hand clap, balloon pop)
- Observe the sound level decay on the graph
- Measure the time it takes for the sound to decay by 60 dB (RT60) or estimate by extrapolation
- Compare different rooms: classroom, gymnasium, hallway
Scientific activities on this topic
- Compare the acoustics of different spaces
- Study the effect of absorbing materials on reverberation
- Measure the acoustics of a concert hall vs a classroom
Learn more
Reverberation time (RT60):
The reverberation time RT60 is the time required for the sound level to decay by 60 dB after the source stops. It is the main parameter for characterizing the acoustics of a room.
Typical values:
| Room type | RT60 (s) |
|---|---|
| Recording studio | 0.2 - 0.4 |
| Classroom | 0.4 - 0.8 |
| Concert hall | 1.5 - 2.5 |
| Cathedral | 4 - 10 |
| Anechoic chamber | ~ 0 |
Reverberation vs echo:
An echo is a distinct reflection perceived after a notable delay (> 50 ms). Reverberation is the sum of multiple reflections so closely spaced that they merge into a continuous decay.
Sabine’s formula:
Wallace Sabine established in 1898 the first formula relating RT60 to the room volume and surface absorption.
Formula
Sabine’s formula:
RT60 = 0.16 x V / A
where:
- RT60: reverberation time (s)
- V: room volume (m^3)
- A: equivalent absorption area (m^2) = sum(alpha_i x S_i)
- alpha_i: absorption coefficient of material i (0 to 1)
- S_i: surface area of material i (m^2)
Application examples
- A classroom with too much reverberation impairs speech intelligibility
- Concert halls are designed for optimal RT60 according to repertoire (shorter for baroque music, longer for romantic)
- Acoustic panels absorb sounds and reduce reverberation
- Music applications add artificial reverberation to simulate different spaces
FAQ
Q: Why does reverberation change depending on the room? A: It depends on volume (larger = more reverberation) and materials (hard surfaces = reflection, soft surfaces = absorption).
Q: How can reverberation be reduced? A: By adding absorbing materials: curtains, carpet, acoustic panels, upholstered furniture.
Q: Can RT60 be measured with FizziQ? A: You can estimate the sound decay time, but precise RT60 measurement requires a sufficient initial sound level to observe a 60 dB drop, which is difficult without professional equipment. RT30 is often measured and extrapolated.
Q: Is reverberation always undesirable? A: No! Appropriate reverberation enriches music and gives a sense of space. Only excess is problematic for speech.
Related concepts
Echo - Sound reflection - Acoustic absorption - Sound level - Decibel - Architectural acoustics